The invention is based on a fuel injection device for internal combustion engines. In one such fuel injection device, known from European Patent Disclosure EP 0 657 642, a high-pressure fuel pump pumps fuel from a low-pressure chamber into a high-pressure collection chamber, which communicates via injection lines with the individual injection valves that protrude into the combustion chamber of the engine to be supplied; this common pressure storage system (common rail) is kept at a certain pressure level by a pressure control device. To control the injection times and quantities at the injection valves, an electrically triggered control valve is provided on each of the injection valves and with its opening and closing it controls the high-pressure fuel injection at the injection valve. The control valve of the known fuel injection device is embodied as a 3/2-way valve, which connects a high-pressure conduit, discharging at the injection port of the injection valve, with the injection line leading away from the high-pressure collection chamber or with a relief line into a low-pressure chamber. In this way, it is attained that the high fuel pressure present in the common high-pressure collection chamber and in the injection lines will not act upon the injection valve during the intervals between injections, so that its closing forces can be correspondingly less, with high system safety, because of the pressure relief of the high-pressure line.
Since in the known fuel injection device the 3/2-way control valve is actuated directly by the actuator of an electrically triggered magnet valve, the known fuel injection device has the disadvantage that the stroke course of the magnet valve defines the adjusting motion at the valve slide of the 3/2-way control valve. Furthermore, the closing force at the 3/2-way control valve, which counteracts the high fuel pressure, is brought to bear solely by the restoring spring of the magnet valve, so that this spring holding force of the magnet valve limits the maximum system pressure in the high-pressure fuel portion, which pressure prevails at the control valve, to a value that no longer meets current needs.
The fuel injection device according to the invention for internal combustion engines, has the advantage over the prior art that the electrically actuated magnet valve actuates the control valve member of the 3/2-way control valve with the interposition of a hydraulic work chamber. A hydraulic stepup at the valve member of the control valve can be achieved by how the face or surface area of the control valve member that defines the hydraulic work chamber is designed, so that this valve acts like a servo piston. In this way, the adjustment path of the control valve member of the 3/2-way control valve becomes independent of the stroke of the magnet valve, and the hydraulic work chamber at the same time performs the restoring function of the control valve member, so that even very high system pressures of over 2000 bar in the high-pressure fuel portion are possible. Furthermore, the pressure in the work chamber, with a buildup of the system pressure, keeps the control valve in a position that closes the flow between the injection line and the high-pressure conduit, so that with a very high effective closing pressure, it is possible to dispense with an additional closing spring.
The hydraulic work chamber at the control valve is advantageously defined by an upper end face of the pistonlike valve member of the control valve and is constantly supplied with fuel at high pressure from the injection line via a throttle cross section between the control valve member and the bore wall that guides it. In addition, on the side remote from the valve member of the control valve, a relief line leads away from the hydraulic work chamber; this line can be opened and closed by the magnet valve. This relief line advantageously has a greater cross section than the throttle cross section to the injection line, so that the pressure in the hydraulic work chamber can be very rapidly relieved upon opening of the relief line.
The control valve is advantageously embodied as a double seat valve, the two valve seat faces of which are oriented toward one another, so that the adjusting motion of the control valve member is limited in each case by contact with one of the valve seats, which reduces possible leakage losses to a minimum. The throttle distance between the injection line and the hydraulic work chamber is formed, in a first exemplary embodiment, by a throttle bore in the control valve member. Alternatively, however, this throttling distance may also be formed by a residual throttling annular gap between the wall of the pistonlike control valve member and the bore wall guiding it.
The region of the control valve member adjoining the second valve seat between the high-pressure conduit and a relief line is guided in sliding fashion along the wall of the receiving bore and thus forms a guide for the control valve member. For a fuel overflow into the relief line, overflow openings on the control valve member are provided, which may be formed for instance by means of a surface chamfer on the control valve member or by suitable through bores.
A further advantage can be attained by providing a stroke-controlled throttle between the first and second sealing seats of the control valve, by which seats the quantity of fuel overflowing from the injection line to the high-pressure conduit is throttled in a first phase of the injection event.
The provision of a restriction in the relief line can moreover reinforce the closing of the injection valve at the end of injection and avert possible dribbles after injection. In addition, by means of this outflow throttle, the residual pressure at the injection valve after the termination of the fuel injection is controlled in such a way that cavitation in the high-pressure conduit can be avoided.
It is thus possible with the fuel injection device of the invention, with relatively low actuating forces and relatively short strokes of the magnet valve, to control large supply quantities and high pressures at the injection valve.
Further advantages and advantageous features of the subject of the invention can be learned from the specification, claims and drawing.